Methods For Preventing Proppant Carryover From Fractures, And Gravel-Packed Filters

ABSTRACT

This invention relates to the oil and gas industry, in particular, to methods affecting the formation productivity at the oil and gas production stage. 
     A method for fracture propping in a subsurface layer, which ensures a reliable protection of wells from the proppant carryover from the fracture, has been proposed. According to the proposed method, a fracturing fluid is mixed with a propping agent and particulate binding material wherein the particles have an average length-to-width ratio of less than or equal to about 10; thereafter, a formation fracturing process is implemented. Then, the particulate binding material hardens and forms a homogenous firm mass with the propping agent, which impedes the closing of the fracture and precludes proppant carryover from the fracture. Or, a fracturing fluid composition obtained by mixing a propping agent with a binding compound in the form of a powder whose size varies from about 1 to about 500 μm. A gravel-packed filter is then constructed; the said filter is based on the application of the working fluid comprising a propping filler and particulate binder with a length-to-width ratio of less than or equal to 10, or comprising a propping filler and a binding compound in the form of a powder with a size varying from about 1 to about 500 micrometers.

This application claims foreign priority benefits to Russian PatentApplication No. 2006146962, filed on Dec. 28, 2006.

FIELD OF THE INVENTION

This invention relates to the oil and gas industry, in particular, tomethods affecting the formation productivity at the oil and gasproduction stage.

BACKGROUND OF THE INVENTION

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

A carryover of proppant from a fracture to the well at thepost-fracturing period either during the initial cleaning or even aftercompletion of the well construction is a crucial issue for the oilproduction sector. Up to 20% of proppant can be conveyed into the well,which, can lead to negative consequences. In marginal wells, proppantsettles in a casing; thus, regular washings are required and the cost ofwell repair operations grows. Premature wear and failure of electricalsubmersible pumps is another consequence of the carryover of unboundproppant or other solid particles of rocks. Also, oil or gas productiondecreases occur due to a significant loss of the near wellboreconductivity caused as a result of a reduced fracture thickness oroverlapping of a production zone.

At present, several methods to decrease in the carryover of proppant orother propping agents from the facture are known.

The most common approach is based on the application of proppant with ahardening resin coating, which is injected into the fracture at the endof the treatment process. However, the use of this type of proppantproduces undesired chemical reactions of the resin coating with thefracturing fluid. This interaction causes partial degradation anddisintegration of the coating, thus reducing the contact strength amongproppant particles and, therefore, decreasing the proppant packstrength. Further, the interaction between the resin coating componentsand fracturing fluid components causes uncontrolled changes in therheological properties of the fluid, which also diminishes thefracturing process efficiency. Extended well closure periods couldsignificantly reduce the proppant filler strength.

In another method, fibrous materials are mixed with a propping agent andadded to limit proppant conveyance; in this process, the combination offibers and proppant particles increase the proppant strength andrestrict the back-flow carryover of the proppant. The addition of fibersenables a more effective redistribution of loads of the proppant. Afibrous structure is more flexible as compared to cured resin proppantand allows movements of proppant-fibrous filler without deterioration ofstrength.

In another method, fiber bundles comprising about 5 to 200 separatefibers are used. In this process, the fiber bundle structure may befixed on one side.

Mixing proppant with deformable beads or particles is also known. Thedeformable particles are polymeric and may have various shapes; however,a maximum length-to-base ratio of equal to or less than 5 is preferable.Deformable particles can be homogeneous spheres formed from one compoundor may be composite particles containing a non-deformable core and adeformable coating. In another embodiment, the core consists ofdeformable materials and could include milled or crushed materials,e.g., nutshell, seed shell, fruits kernels and processed wood.

Mixtures of proppant with adhesive polymeric materials have also beenused. The adhesive compositions contain and cover the particles with athin sticky layer. As a result, particles adhere to each other as wellas to sand particles or crushed fragments of the propping agent. Thiscompletely prevents the carryover of solid particles from the fracture.Adhesive materials can also be combined with other chemical agents usedin the formation fracturing process, e.g., retarding agents,antimicrobial agents, polymer gel destructors, as well as antioxidantand wax-formation and corrosion retarding agents. Mixtures of adhesivematerials with deformable particles have also been used.

Thermoplastic materials have also been used with proppants. When mixedwith a propping agent, the thermoplastics soften upon exposure to hightemperatures, and thereafter they adhere to the propping agent to formaggregates. Thermoplastic agents may also be used with resin proppants.

Another method describes the application of a fracturing fluid which isa self-degrading cement comprising an acid, which interacts with othercomponents to cause the formation of a cement material, as well as adegrading component, which could disintegrate under the fractureconditions and cause the formation of cavities in the cement.

Another method describes the formation fracturing process using ahydrated cement particles with average particle sizes ranging from 5 μmto 2.5 cm.

SUMMARY OF THE INVENTION

The invention provides methods for fracture propping in the oil and gasindustry, in particular, to the development of a method for preventingcarryover of proppant from fractures.

Specifically, the invention provides methods for fracture propping in ansubterranean formation which provides reliable protection of the wellfrom excess proppant conveyance from the fracture.

Specifically, the invention provides a method in which a formationfracturing fluid is mixed with a filler component comprising at leastone propping agent and at least one particulate binder wherein theparticulate binder particles have an average length-to-width ratio ofequal to or less than about 10, and thereafter, a formation fracturingprocess is implemented. The particulate binding material is thensolidified to form a homogeneous firm mass with the propping agent,which obstructs the closure of the fracture and precludes the proppantcarryover.

The invention further provides fracturing fluid compositions obtained bymixing a propping filler and a particulate binder with a length-to-widthratio of equal to or less than 10, which could solidify underunderground formation conditions.

The invention further provides fracturing fluid compositions obtained bymixing a propping filler and a particulate binding composition in theform of a powder, whose size varies from about 1 μm to about 500 μm. Inthis case, powder-like particles of the binder get into contact with thepropping filler and are then solidified, increasing the propping fillerpack strength.

In one embodiment, the fracturing fluid compositions are obtained bymixing a propping filler and a particulate or powder binding material aswell as other components obstructing the proppant conveyance from thefracture, including deformable particles and adhesive and fiber-likematerials.

The invention further provides a gravel-packed filter which is based onthe application of a working fluid comprising a propping filler and aparticulate binder with a length-to-width ratio of equal to or less than10, or comprising a propping filler and a particulate bindingcomposition in the form of a powder, whose size varies from about 1 μmto about 500 μm.

DETAILED DESCRIPTION OF THE INVENTION

At the outset, it should be noted that in the development of any suchactual embodiment, numerous implementation-specific decisions must bemade to achieve the developer's specific goals, such as compliance withsystem related and business related constraints, which will vary fromone implementation to another. Moreover, it will be appreciated thatsuch a development effort might be complex and time consuming but wouldnevertheless be a routine undertaking for those of ordinary skill in theart having the benefit of this disclosure. The description and examplesare presented solely for the purpose of illustrating the preferredembodiments of the invention and should not be construed as a limitationto the scope and applicability of the invention. While the compositionsof the present invention are described herein as comprising certainmaterials, it should be understood that the composition could optionallycomprise two or more chemically different materials. In addition, thecomposition can also comprise some components other than the onesalready cited. In the summary of the invention and this detaileddescription, each numerical value should be read once as modified by theterm “about” (unless already expressly so modified), and then read againas not so modified unless otherwise indicated in context. Also, in thesummary of the invention and this detailed description, it should beunderstood that a concentration range listed or described as beinguseful, suitable, or the like, is intended that any and everyconcentration within the range, including the end points, is to beconsidered as having been stated. For example, “a range of from 1 to 10”is to be read as indicating each and every possible number along thecontinuum between about 1 and about 10. Thus, even if specific datapoints within the range, or even no data points within the range, areexplicitly identified or refer to only a few specific, it is to beunderstood that inventors appreciate and understand that any and alldata points within the range are to be considered to have beenspecified, and that inventors possession of the entire range and allpoints within the range.

The compositions may contain one or more than one of the below-listedmaterials as propping fillers: ceramic particles and sand particleshaving different shapes, solidified and curable proppants and sands;swollen expanded clay, vermiculite, and agloporite. Further, proppantsor polymer-coated sand can be used as a propping filler.

Granulated and powdered binders can be added in a fracturing fluid in adry state, or in other forms such as suspensions in water, workingfluids, gels or other suitable solvent containing forms, including thosemodified with various surfactants.

Useful binders for particulate binders include but are not limited tothe following. The components may be hardened by hydraulic, air andautoclave hardening and may include acid-proof binding materials andmixtures of such materials.

Useful materials include those based on of crystalline hydrates CaSO₄and anhydrite (gypsum binding materials); materials based on CaO, CaOhydration and carbonization products (lime binding materials) and thelike; materials based on MgO and saline sealers (magnesium bindingmaterials); lime-silica binding materials comprising mixtures of CaO orCa(OH)₂ with fine-milled silica, which solidify at increasedtemperatures; lime-pozzolanic and lime-cindery binding materialscomprising a lime-containing component and a reactive silicic acid inthe form of amorphous silica or silicate glass, whose hardening occursdue to the interaction of a lime with an active silicon oxide or glasswith the formation of calcium hydrosilicates.

Other useful materials include slag-alkali binding materials having acomponent comprising caustic alkali and slag, preferably in a vitreousstate, whose hardening is connected with the formation of alcalinealuminum silicate.

Binding cements such as high-basic calcium silicates (portland cementclinker, natural cement, calcareous cement, hydraulic lime, and thelike) are also useful. The binding properties of these materials areessentially predefined by hydration of tricalcium (Ca₃SiO₅) anddicalcium (Ca₂SiO₄) silicates, including slag-portland cement, cementsbased on low-basic calcium aluminates (CaA, CA₂, C₁₂A₇) and derivatives,thereof, e.g., calcium sulfoaluminates, calcium fluoroaluminates(aluminate cement, high-alumina cement, sulfoaluminate cement); highiron oxide cements and sulfur high iron oxide cements. Cements based oncalcium ferrites and their derivatives such as calcium sulfoferrites mayalso be used.

Phosphate binding materials (cement and binding materials), which hardendue to phosphate formation are also useful.

Watersoluble silicate materials, including but not limited to alkalimetal silicates (soluble glasses) and organic base silicates

Also useful are polymer-cement compositions and polymer-silicate bindingcompositions containing organic compositions as modifying components andinorganic binding materials (cement, soluble glass) as the base;

Hydroxy salts of aluminum, chrome, zirconium, colloidal solution ofsilica and aluminum oxide, partially dehydrated crystalline hydrates ofaluminum sulfates and calcium aluminates may also be used.

A particulate binder may comprise a single component, or have amulti-component composition. In addition to binders, the particulatebinder may include components which improve required strength properties(e.g., polymers) and density properties (e.g., particles of barite, rediron ore, glass beads, porous particles).

The particulate binders can be provided in a variety of shapes,including but not limited to, spherical, cylindrical, sparry, cubic,oval, flaked, scaly, irregular shape, or a combination of theabove-mentioned shapes, so long as the particles have a length-to-widthratio to be equal to or less than about 10.

The content of particulate binding filler in the total volume ofpropping and particulate fillers varies in the range from about 0.1 toabout 99.9% by weight. The actual density of the particulate bindingagent varies in the range from about 0.3 to about 5 g/cm³.

At least one of the following binders of the classes can be used, suchcomponents may be hardened by methods such as hydraulic, air andautoclave hardening as well as acid-proof binding materials as well asmixtures thereof, including but not limited to materials based oncrystalline hydrates CaSO₄ and anhydrite (gypsum binding materials);materials based on CaO, CaO hydrates and carbonization products (limebinding materials); materials on the basis of MgO and saline sealers(magnesium binding materials)

Useful materials include those based on of crystalline hydrates CaSO₄and anhydrite (gypsum binding materials); materials based on CaO, CaOhydration and carbonization products (lime binding materials) and thelike; materials based on MgO and saline sealers (magnesium bindingmaterials); lime-silica binding materials comprising mixtures of CaO orCa(OH)₂ with fine-milled silica, which solidify at increasedtemperatures; lime-pozzolanic and lime-cindery binding materialscomprising a lime-containing component and a reactive silicic acid inthe form of amorphous silica or silicate glass, whose hardening occursdue to the interaction of a lime with an active silicon oxide or glasswith the formation of calcium hydrosilicates.

Other useful materials include slag-alkali binding materials having acomponent comprising caustic alkali and slag, preferably in a vitreousstate, whose hardening is connected with the formation of alcalinealuminum silicate.

Binding cements such as high-basic calcium silicates (portland cementclinker, natural cement, calcareous cement, hydraulic lime, and thelike) are also useful. The binding properties of these materials areessentially predefined by hydration of tricalcium (Ca₃SiO₅) anddicalcium (Ca₂SiO₄) silicates, including slag-portland cement, cementsbased on low-basic calcium aluminates (CaA, CA₂, C₁₂A₇) and derivatives,thereof, e.g., calcium sulfoaluminates, calcium fluoroaluminates(aluminate cement, high-alumina cement, sulfoaluminate cement); highiron oxide cements and sulfur high iron oxide cements. Cements based oncalcium ferrites and their derivatives such as calcium sulfoferrites mayalso be used.

Phosphate binding materials (cement and binding materials), which hardendue to phosphate formation are also useful.

Watersoluble silicate materials, including alkali metal silicates(soluble glasses) and organic base silicates

Also useful are polymer-cement compositions and polymer-silicate bindingcompositions containing organic compositions as modifying components andinorganic binding materials (cement, soluble glass) as the base;

Hydroxy salts of aluminum, chrome, zirconium, colloidal solution ofsilica and aluminum oxide, partially dehydrated crystalline hydrates ofaluminum sulfates and calcium aluminates may also be used.

The average particle size of useful particulate binding materials orbinders ranges from about 0.5 to about 500 μm. The concentration of theparticulate binding materials in the propping filler varies from about0.1 to about 99.9% by weight.

The density of the powder-like binding materials can vary from about 0.5to about 5 g/cm³.

Such granulated or powder-like binding materials will be used in amixture with a propping agent; the concentration of the propping agentin the mixture could vary in the range of about 0.1 to about 99.9%.

The terms granulated, powder-like, and particulate are usedinterchangeably herein. Granulated or powder-like binding materials maybe added to the propping fluid either in a dry state or in other formssuch as suspensions in water, working fluids, gels or other suitablesolutions including those modified by various surfactants.

Embodiments of the invention may use other additives and chemicals thatare known to be commonly used in oilfield applications by those skilledin the art. These include, but are not necessarily limited to, materialsin addition to those mentioned hereinabove, such as breaker aids, oxygenscavengers, alcohols, scale inhibitors, corrosion inhibitors, fluid-lossadditives, bactericides, iron control agents, organic solvents, and thelike. Also, they may include a co-surfactant to optimize viscosity or tominimize the formation of stabilized emulsions that contain componentsof crude oil, or as described hereinabove, a polysaccharide orchemically modified polysaccharide, natural polymers and derivatives ofnatural polymers, such as cellulose, derivatized cellulose, guar gum,derivatized guar gum, or biopolymers such as xanthan, diutan, andscleroglucan, synthetic polymers such as polyacrylamides andpolyacrylamide copolymers, oxidizers such as persulfates, peroxides,bromates, chlorates, chlorites, periodates, and the like. Some examplesof organic solvents include ethylene glycol monobutyl ether, isopropylalcohol, methanol, glycerol, ethylene glycol, mineral oil, mineral oilwithout substantial aromatic content, and the like.

1. A method for preventing proppant carryover from a fracture in asubterranean formation, the method comprising the steps of: a) providinga treatment fluid, b) mixing the treatment fluid with a filler componentcomprising at least one propping agent and at least one particulatebinder having an average particle length-to-width ratio of no more thanabout 10, and c) injecting the fluid into the formation, wherein thefluid solidifies under subterranean formation conditions.
 2. The methodof claim 1, wherein the particulate binder is present in the fillercomponent in an amount of from about 0.1% to about 99.9%.
 3. The methodof claim 1, wherein the filler component comprises at least one materialselected from the group consisting of particulates having been hardenedby a hydraulic hardening, air hardening or autoclave hardening,acid-proof binding materials and mixtures thereof.
 4. The method ofclaim 1, in which the filler component comprises gypsum bindingmaterials.
 5. The method of claim 4 wherein the filler componentcomprises CaSO₄ crystalline hydrates and anhydrites.
 6. The method ofclaim 1, wherein the filler component c comprises lime bindingmaterials.
 7. The method of claim 6, wherein the filler componentcomprises materials selected from calcium oxides and CaO hydration &carbonization products.
 8. The method of claim 1, wherein the fillercomponent comprises magnesium binding materials
 9. The method of claim8, wherein the filler component comprises magnesium oxide or a salinesealer.
 10. The method of claim 1, wherein the filler componentcomprises a lime-silica material comprising a mixture of CaO or Ca(OH)₂with fine-milled silica which is capable of hardening at subterraneanformation temperatures.
 11. The method of claim 1, wherein the fillercomponent comprises lime-pozzolanic and lime-slag materials.
 12. Themethod of claim 1, wherein the filler component compriseslime-containing components or reactive silicic acid in the form ofamorphous silica or silicate glass, whose hardening is caused by theinteraction of lime with active silica or glass with the formation ofcalcium hydrosilicates.
 13. The method of claim 1, wherein the fillercomponent comprises i slag-alkali binders comprising a constituent thatincludes a caustic alkali and slag, in a vitreous state, and whosehardening proceeds with the formation of alcaline aluminum silicates.14. The method of claim 1, wherein the filler component comprises cementbased on high-basic calcium silicates.
 15. The method of claim 1 whereinthe filler component comprises at least cement based on calciumaluminate (CaA, CA₂, C₁₂A₇), calcium sulfoaluminates, calciumfluoroaluminates (calcium aluminate cement, high-alumina cement,sulfoaluminate cement) or iron & sulfur-iron cements.
 16. The method ofclaim 1, wherein the filler component comprises calcium ferrites orcalcium sulfur ferrite cements, portland cement, roman cement,calcareous lime or mixtures thereof.
 17. The method of claim 1, whereinthe particulate binding component comprises phosphates.
 18. The methodof claim 1, wherein the filler component comprises watersolublesilicates.
 19. The method of claim 1, wherein the filler componentcomprises polymer-cement or polymer-silicate compositions comprisingorganic compounds as modifying agents and inorganic compounds as thebase.
 20. The method of claim 1, wherein the filler component comprisesat least one compound selected from the group consisting of hydroxysalts of alumina, chrome, zirconium, colloidal silica solutions, partlydehydrated crystalline hydrates of aluminum sulfates and calciumaluminates.
 21. The method of claim 1, wherein at least one of thetreatment fluid or the filler component further comprises at least oneas additive selected from the group consisting of polymers, bariteparticles, red iron ore, glass beads, porous particles, sand withpolymeric coating, ceramic particles, sand, cured or curable proppantsand sands, swollen expanded clay, vermiculite, agloporite, deformableparticles, adhesive materials and fibrous materials.
 22. The method ofclaim 1 wherein said filler component comprises at least one particulatefiller having an average particle size of from 0.5 to 500 μm.
 23. Themethod of claim 1, in which the density of the particulate binder variesfrom 0.5 to approximately 5 g/cm³.
 24. A method of fracturing asubterranean formation, the method comprising the steps of: a) providinga treatment fluid, b) mixing the treatment fluid with a filler componentcomprising at least one propping agent and at least one particulatebinder having an average particle length-to-width ratio of no more thanabout 10, and c) injecting the fluid into the formation, and d)fracturing the formation, wherein the fluid solidifies undersubterranean formation conditions.
 25. A gravel-packed filter obtainedby application of a method according to claim 1.